Abstract: To investigate the vertical distribution of root biomass（diameter≤2 mm） and root length density of Pinus tabulaeformis and Cupressus chengiana plantations in the arid valleys of the upper Minjiang River, and to analyze the carbon allocation strategy of fine root system in different soil layers, and to provide reference for vegetation restoration in the arid valleys of the upper Minjiang River. P. tabulaeformis and C. chengiana plantations were sampled by soil corer method, and the root biomass and root length density of absorptive roots（first to third order） and transport roots（≥fourth order） in different depth（h）（0 cm＜h≤15 cm and 15 cm＜h≤30 cm） were measured, as well as the proportions biomass and length density of absorptive roots to the total fine roots.The results showed that: the absorptive root biomass and root length density of P. tabulaeformis and C.chengiana were significantly higher in 0 cm＜h≤15 cm than those in 15 cm＜h≤30 cm, and the transport root biomass and root length density were not significantly different between soil layers; the proportions biomass and length density of absorptive roots to the total fine roots in 0 cm＜h≤15 cm were significantly higher than that in 15 cm＜h≤30 cm（P＜0.05）; the proportions biomass and length density of absorptive roots to the total fine roots in 0 cm＜h≤15 cm and 15 cm＜h≤30 cm of C. chengiana were significantly higher than those of P. tabulaeformis（P＜0.05）. These findings suggested that more carbon was allocated to the absorptive roots in the surface soil layers with the highest nutrient availability in P. tabulaeformis and C. chengiana root system.